Surfacing and/or joining method

ABSTRACT

A method for surfacing a polymeric composite article and/or for joining (for example, by bonding or by co-curing) the article and an adherend (for example, a second polymeric composite article) comprises
         (a) providing a cured or curable polymeric composite article;   (b) providing a curable composition comprising
           (1) at least one thermosetting resin, and   (2) at least one preformed, substantially non-functional, particulate modifier comprising at least one elastomer;   and   
           (c) directly or indirectly applying the composition to at least a portion of at least one surface of the article.

FIELD

This invention relates to methods for surfacing polymeric compositearticles and for joining (for example, by bonding or by co-curing) sucharticles and various substrates. In another aspect, this invention alsorelates to surfaced structures and joined structures prepared thereby.

BACKGROUND

Adhesives have been used in many structural applications including usein constructing vehicles, computer cases, buildings, appliances, and thelike. For example, structural adhesives have been used in vehicleassembly (for example, automobile and aircraft assembly) to replace oraugment conventional joining techniques such as welds, nuts and bolts,and rivets.

Epoxide resins are monomers or pre-polymers that react with curingagents to yield high performance cured resins. The cured resins exhibitnumerous desirable chemical and physical characteristics (for example,thermal and chemical resistance, adhesion retention, low shrinkage,abrasion resistance, and high dielectric strength) and are widelyutilized (for example, in the construction and electronics industries)as protective coatings for electrical insulation, as composite matrixresins, and as structural adhesives.

Frequently, it is desired that the cured epoxy resins have a relativelyhigh glass transition temperature (T_(g)), so as to be strong atrelatively high temperatures. A common method of increasing the glasstransition temperature has been by introducing a high degree ofcrosslinking.

Cured resins having a high crosslink density have had shortcomings,however. For example, such resins have typically been very brittle (thatis, not very tough or ductile). Thus, it has often been necessary ordesirable to incorporate various resin-insoluble modifiers to reducebrittleness and increase toughness (thereby increasing impactresistance, as well as resistance to failure resulting from vibrationand fatigue loading).

In addition to exhibiting brittleness problems, the cured resins havesometimes exhibited undesirable moisture uptake characteristics(especially when a high concentration of polar groups has beenutilized), resulting in reduced structural adhesive performance.

SUMMARY

Thus, we recognize that there is a continuing need for higherperformance adhesives in order to meet the changing needs of variousindustries such as, for example, the vehicle assembly industry. Inparticular, for the joining of polymeric composite parts in the aircraftindustry, we recognize that there is a need for joining methods that canprovide high performance joints, even in the presence of significantprebond humidity.

Briefly, in one aspect, the present invention provides a method forsurfacing a polymeric composite article (for example, to reduce oreliminate surface imperfections and provide a more paintable surface)and/or for joining (for example, by bonding or by co-curing) the articleand an adherend (for example, a second polymeric composite article). Themethod comprises

-   -   (a) providing a cured or curable polymeric composite article;    -   (b) providing a curable composition comprising        -   (1) at least one thermosetting resin, and        -   (2) at least one preformed, substantially non-functional,            particulate modifier comprising at least one elastomer;        -   and    -   (c) directly or indirectly applying the composition to at least        a portion of at least one surface (preferably, a composite        surface) of the article.        Preferably, the article is a cured polymeric composite article,        the thermosetting resin is an epoxide resin, and/or the modifier        is a core-shell polymer modifier. The method preferably further        comprises bringing at least a portion of at least one surface of        at least one adherend into contact with the composition in a        manner such that the composition becomes sandwiched between the        article and the adherend, and/or at least partially curing the        composition.

It has been discovered that thermosetting compositions comprisingcertain types of particulate modifiers can be used as surfacingmaterials and/or to form high performance joints between polymericcomposite parts and various adherends (including, for example, othercured or curable polymeric composite parts). Surprisingly, suchcompositions exhibit an ability to resist the negative effects ofprebond humidity (including, for example, the negative effects of themoisture content of the article at the time of surfacing or joining).

Such negative effects can include a reduction in cohesive strength (forexample, due to a lowering of glass transition temperature (T_(g))), areduction in cure rate, and/or a reduction in toughness (for example,due to morphology changes). Relative to structural adhesives commonlyused in the aerospace industry, the compositions can show significantlyimproved retention of performance characteristics without the need forprebond conditioning (for example, drying).

Thus, at least some embodiments of the method of the invention meet theabove-stated need in the art for joining methods that can provide highperformance joints, even in the presence of significant prebondhumidity. The ability to provide such joints can enable reliable andconsistent parts manufacture and can reduce the costly need forrestrictive temperature and humidity control of preformed parts (andpart assembly areas) in aircraft assembly.

In another aspect, this invention also provides a surfaced or joinedstructure comprising

-   -   (a) a cured or curable polymeric composite article; and    -   (b) a cured or curable composition comprising        -   (1) at least one thermosetting resin, and        -   (2) at least one preformed, substantially non-functional,            particulate modifier comprising at least one elastomer;            the composition being in contact with at least a portion of            at least one surface (preferably, a composite surface) of            the article. Preferably, the structure is a joined structure            that further comprises at least one adherend that is joined            to the article by at least one joint comprising the cured            composition.

DETAILED DESCRIPTION Definitions

As used in this application:

“cure” means to effect polymerization and/or to effect crosslinking (asevidenced, for example, by a change in density, viscosity, modulus,color, pH, refractive index, or other physical or chemical property);

“co-cure” (in reference to the joining of a polymeric composite articleand an adherend by using a curable composition) means to simultaneouslyeffect at least partial cure of the curable composition and at leastpartial cure of the article and/or the adherend;

“bond” (in reference to the joining of a polymeric composite article andan adherend by using a curable composition) means to join by a techniqueother than co-curing;

“cured” means that a sufficient number of the primary polymerizable orcrosslinkable functional groups of a thermosetting resin (for example,the epoxide groups of an epoxide resin) have been consumed throughchemical reaction to enable the resin to function for its intendedpurpose;

“preformed” (in reference to a particulate modifier as a component of acurable composition comprising thermosetting resin) means formed priorto initiation of the curing of the thermosetting resin as discreteparticles that substantially maintain their discreteness during andafter curing; and

“substantially non-functional” (in reference to a particulate modifieras a component of a curable composition comprising thermosetting resin)means bearing essentially no functional groups that are capable of both(1) contact and (2) chemical reaction with the thermosetting resin.

Polymeric Composite Article

Polymeric composite articles (also sometimes called composite parts) areknown and include articles that comprise reinforcing fibers (forexample, carbon or glass) embedded in an organic resin matrix (forexample, comprising a thermosetting resin that can be cured to form aglassy network polymer). Polymeric composite articles can be as simpleas one or more layers of curable (that is, uncured or partially cured)resin-impregnated fiber or fabric (such single- or multi-layerstructures being termed “prepreg”), or they can be as complex assandwich constructions comprising a metallic or non-metallic honeycombcore and prepreg or cured prepreg. Articles typically used in structuralapplications include composite stringers, composite skin, and the like,which can be used to construct flaps, alirons, radomes, horizontal orvertical stabilizers, wings, and other portions of aircraft.

Suitable thermosetting resins for use in making composite articlesinclude, for example, epoxide resins, curable imide resins (especiallymaleimide resins, but also including, for example, commercial K-3polyimides (available from duPont) and polyimides having a terminalreactive group such as acetylene, diacetylene, phenylethynyl,norbornene, nadimide, or benzocyclobutane), vinyl ester resins andacrylic resins (for example, (meth)acrylic esters or amides of polyols,epoxides, and amines), bisbenzocyclobutane resins, cyanate ester resins,phenolic resins (including nitrile phenolics), and the like, andmixtures thereof. The resins can be utilized in the form of eithermonomers or prepolymers. Thermoplastic resins (for example,polysulfones, poly(ether-ether-ketone) (PEEK), polyphenylene sulfide,polyamides, polyethersulfone, polyetherimides, polycarbonates, and thelike, and mixtures thereof) can also be utilized.

Preferred resins include thermosetting resins (more preferably, epoxideresins, maleimide resins, cyanate ester resins, and the like, andmixtures thereof). Epoxide resins are most preferred due to theirprocessing characteristics, high temperature properties, andenvironmental resistance.

Suitable reinforcing fibers (preferably, continuous reinforcing fibers)for use in preparing composite articles include both organic andinorganic fibers (for example, carbon or graphite fibers, glass fibers,ceramic fibers, boron fibers, silicon carbide fibers, cellulose fibers,polyimide fibers, polyamide fibers, polyethylene fibers, and the like,and combinations thereof). Fibers of carbon, glass, or polyamide can bepreferred due to considerations of cost, physical properties, andprocessability. Such fibers can be in the form of, for example, aunidirectional array of individual continuous fibers, woven fabric,knitted fabric, yarn, roving, braided constructions, or non-woven mat.Generally, the compositions can contain, for example, from about 30 toabout 80 (preferably, from about 45 to about 70) volume percent fibers,depending upon structural application requirements.

Useful fiber-containing resin compositions can further compriseadditives such as curing agents, cure accelerators, catalysts,crosslinking agents, dyes, flame retardants, pigments, impact modifiers(for example, rubbers or thermoplastics), flow control agents, and thelike, and mixtures thereof.

Composite articles can be made by a variety of conventional processesincluding, for example, resin transfer molding, filament winding, towplacement, resin infusion processes, and traditional prepreg processes.Prepregs can be prepared by impregnating an array of fibers (or afabric) with a resin (or with a blend or solution of resin in volatileorganic liquid) and then layering the impregnated tape or fabric. Theresulting prepreg can then be cured by application of heat, along withthe application of pressure or vacuum (or both) to remove any trappedair.

Composite parts can also be made by a resin transfer molding process,which is widely used to prepare composite parts for the aerospace andautomotive industries. In this process, fibers can first be shaped intoa preform that can then be compressed to final part shape in a metalmold. The resin can then be pumped into the mold and heat-cured. A lowresin viscosity can facilitate this process in that such a resin canflow through the compressed preform in a short amount of time, withoutpreform distortion.

A filament winding process is typically used to prepare cylinders orother composites having a circular or oval cross-sectional shape. Inthis process, a fiber tow or an array of tows can be impregnated withresin by running it through a resin bath (preferably, containing a lowviscosity resin) and immediately winding the impregnated tow onto amandrel. The resulting composite can then be heat-cured.

A pultrusion process (a continuous process used to prepare constantcross-section parts) can also be used to make composites. In such aprocess, a large array of continuous fibers can first be wetted out in aresin bath (preferably, containing a low viscosity resin). The resultingwet array can then be pulled through a heated die, where trapped air canbe squeezed out and the resin cured.

Curable Composition

(1) Thermosetting Resin

Resins suitable for use in preparing the curable composition of themethod of the invention include thermosetting resins. Such resins can becured by exposure to heat or radiation to form a glassy network polymer.Suitable resins include, for example, epoxide resins, curable imideresins (especially maleimide resins, but also including, for example,commercial K-3 polyimides (available from duPont) and polyimides havinga terminal reactive group such as acetylene, diacetylene, phenylethynyl,norbornene, nadimide, or benzocyclobutane), vinyl ester resins andacrylic resins (for example, (meth)acrylic esters or amides of polyols,epoxides, and amines), bisbenzocyclobutane resins, cyanate ester resins,and the like, and mixtures thereof. The resins can be utilized in theform of either monomers or prepolymers. Preferred resins include epoxideresins, maleimide resins, cyanate ester resins, and the like, andmixtures thereof. Epoxide resins are especially preferred due to theirprocessing characteristics, high temperature properties, andenvironmental resistance.

Epoxide resins are well-known in the art and comprise compounds ormixtures of compounds that contain one or more epoxide groups of thestructure

The compounds can be saturated or unsaturated, aliphatic, alicylic,aromatic, or heterocyclic, or can comprise combinations thereof.Compounds that contain more than one epoxide group (that is,polyepoxides) are preferred.

Polyepoxides that can be utilized in the curable composition of themethod of the invention include, for example, both aliphatic andaromatic polyepoxides, but aromatic polyepoxides are preferred for hightemperature applications. The aromatic polyepoxides are compoundscontaining at least one aromatic ring structure (for example, a benzenering) and more than one epoxide group. Preferred aromatic polyepoxidesinclude the polyglycidyl ethers of polyhydric phenols (for example,bisphenol A derivative resins, epoxy cresol-novolac resins, bisphenol Fderivative resins, epoxy phenol-novolac resins), glycidyl esters ofaromatic carboxylic acids, glycidyl amines of aromatic amines, and thelike, and mixtures thereof. The most preferred aromatic polyepoxides arethe polyglycidyl ethers of polyhydric phenols.

Representative examples of aliphatic polyepoxides that can be utilizedin the curable composition include3′,4′-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate,2-(3′,4′-epoxycyclohexyl)-5,1″-spiro-3″,4″-epoxycyclohexane-1,3-dioxane,bis(3,4-epoxycyclohexylmethyl)adipate, the diglycidyl ester of linoleicdimer acid, 1,4-bis(2,3-epoxypropoxy)butane,4-(1,2-epoxyethyl)-1,2-epoxycyclohexane,2,2-bis(3,4-epoxycyclohexyl)propane, polyglycidyl ethers of aliphaticpolyols such as glycerol or hydrogenated4,4′-dihydroxydiphenyl-dimethylmethane, and the like, and mixturesthereof.

Representative examples of aromatic polyepoxides that can be utilized inthe curable composition include glycidyl esters of aromatic carboxylicacids (for example, phthalic acid diglycidyl ester, isophthalic aciddiglycidyl ester, trimellitic acid triglycidyl ester, pyromellitic acidtetraglycidyl ester, and the like, and mixtures thereof);N-glycidylaminobenzenes (for example, N,N-diglycidylbenzeneamine,bis(N,N-diglycidyl-4-aminophenyl)methane,1,3-bis(N,N-diglycidylamino)benzene,N,N-diglycidyl-4-glycidyloxybenzeneamine, and the like, and mixturesthereof); the polyglycidyl derivatives of polyhydric phenols (forexample, the polyglycidyl ethers of polyhydric phenols such as2,2-bis-[4-hydroxyphenyl]propane, tetrakis(4-hydroxyphenyl)ethane,pyrocatechol, resorcinol, hydroquinone, 4,4′-dihydroxydiphenyl methane,4,4′-dihydroxydiphenyl dimethyl methane,4,4′-dihydroxy-3,3′-dimethyldiphenyl methane, 4,4′-dihydroxydiphenylmethyl methane, 4,4′-dihydroxydiphenyl cyclohexane,4,4′-dihydroxy-3,3′-dimethyldiphenyl propane, 4,4′-dihydroxydiphenylsulfone, and tris-(4-hydroxyphenyl)methane); polyglycidyl ethers ofnovolacs (reaction products of monohydric or polyhydric phenols withaldehydes in the presence of acid catalysts), and the derivativesdescribed in U.S. Pat. Nos. 3,018,262 (Schoeder) and 3,298,998 (Cooveret al.), the descriptions of which are incorporated herein by reference,as well as the derivatives described in the Handbook of Epoxy Resins byLee and Neville, McGraw-Hill Book Co., New York (1967) and in EpoxyResins, Chemistry and Technology, Second Edition, edited by C. May,Marcel Dekker, Inc., New York (1988); and the like; and mixturesthereof. A preferred class of polyglycidyl ethers of polyhydric phenolsfor use in the curable composition are the diglycidyl ethers ofbisphenol that have pendant carbocyclic groups (for example, thosedescribed in U.S. Pat. No. 3,298,998 (Coover et al.), the description ofwhich is incorporated herein by reference). Examples of such compoundsinclude 2,2-bis[4-(2,3-epoxypropoxy)phenyl]norcamphane and2,2-bis[4-(2,3-epoxypropoxy)phenyl]decahydro-1,4,5,8-dimethanonaphthalene.Preferred compounds include dicyclopentadiene-containing polyepoxides(for example, TACTIX 756 and TACTIX 556, available from HuntsmanAdvanced Materials Americas, Inc., Brewster, N.Y.).

Suitable epoxide resins can be prepared by, for example, the reaction ofepichlorohydrin with a polyol, as described, for example, in U.S. Pat.No. 4,522,958 (Das et al.), the description of which is incorporatedherein by reference, as well as by other methods described by Lee andNeville and by May, supra. Many epoxide resins are also commerciallyavailable.

Maleimide resins suitable for use in the curable composition of themethod of the invention include bismaleimides, polymaleimides, andpolyaminobismaleimides. Such maleimides can be conveniently synthesizedby combining maleic anhydride or substituted maleic anhydrides with di-or polyamine(s). Preferred are N,N′-bismaleimides, which can beprepared, for example, by the methods described in U.S. Pat. Nos.3,562,223 (Bargain et al.), 3,627,780 (Bonnard et al.), 3,839,358(Bargain), and 4,468,497 (Beckley et al.) (the descriptions of which areincorporated herein by reference) and many of which are commerciallyavailable.

Representative examples of suitable N,N′-bismaleimides include theN,N′-bismaleimides of 1,2-ethanediamine, 1,6-hexanediamine,trimethyl-1,6-hexanediamine, 1,4-benzenediamine,4,4′-methylenebisbenzenamine, 2-methyl-1,4-benzenediamine,3,3′-methylenebisbenzenamine, 3,3′-sulfonylbisbenzenamine,4,4′-sulfonylbisbenzenamine, 3,3′-oxybisbenzenamine,4,4′-oxybisbenzenamine, 4,4′-methylenebiscyclohexanamine,1,3-benzenedimethanamine, 1,4-benzenedimethanamine,4,4′-cyclohexanebisbenzenamine, and the like, and mixtures thereof.

Co-reactants for use with the bismaleimides can include any of a widevariety of unsaturated organic compounds, particularly those havingmultiple unsaturation, either ethylenic, acetylenic, or both. Examplesinclude acrylic acids and amides and the ester derivatives thereof, forexample, acrylic acid, methacrylic acid, acrylamide, methacrylamide, andmethylmethacrylate; dicyanoethylene; tetracyanoethylene; allyl alcohol;2,2′-diallylbisphenol A; 2,2′-dipropenylbisphenol A; diallylphthalate;triallylisocyanurate; triallylcyanurate; N-vinyl-2-pyrrolidinone;N-vinyl caprolactam; ethylene glycol dimethacrylate; diethylene glycoldimethacrylate; trimethylolpropane triacrylate; trimethylolpropanetrimethacrylate; pentaerythritol tetramethacrylate;4-allyl-2-methoxyphenol; triallyl trimellitate; divinyl benzene;dicyclopentadienyl acrylate; dicyclopentadienyloxyethyl acrylate;1,4-butanediol divinyl ether; 1,4-dihydroxy-2-butene; styrene; α-methylstyrene; chlorostyrene; p-phenylstyrene; p-methylstyrene;t-butylstyrene; phenyl vinyl ether; and the like; and mixtures thereof.Of particular interest are resin systems employing a bismaleimide incombination with a bis(alkenylphenol). Descriptions of a typical resinsystem of this type can be found in U.S. Pat. No. 4,100,140 (Zahir etal.), the descriptions of which are incorporated herein by reference.Particularly preferred components are 4,4′-bismaleimidodiphenylmethaneand o,o′-diallyl bisphenol A.

Cyanate ester resins suitable for use in the curable composition of themethod of the invention can be prepared by combining cyanogen chlorideor bromide with an alcohol or phenol. The preparation of such resins andtheir use in polycyclotrimerization to produce polycyanurates aredescribed in U.S. Pat. No. 4,157,360 (Chung et al.), the descriptions ofwhich are incorporated herein by reference. Representative examples ofsuitable cyanate ester resins include 1,2-dicyanatobenzene,1,3-dicyanatobenzene, 1,4-dicyanatobenzene,2,2′-dicyanatodiphenylmethane, 3,3′-dicyanatodiphenylmethane,4,4′-dicyanatodiphenylmethane, and the dicyanates prepared from biphenolA, bisphenol F, and bisphenol S, and the like, and mixtures thereof.Tri- and higher functionality cyanate ester resins are also suitable.

(2) Particulate Modifier

Particulate modifiers that are suitable for use in preparing the curablecomposition of the method of the invention include preformed,substantially non-functional particulate modifiers that comprise atleast one elastomer. Such modifiers preferably comprise both a rubberyphase (for example, having a glass transition temperature (T_(g)) lessthan or equal to about 0° C. (preferably, less than or equal to about−20° C.)) and a thermoplastic or glassy phase (for example, having aglass transition temperature above about 25° C. (preferably, above about50° C.)). The rubbery phase can optionally be crosslinked. Although themodifiers are substantially non-functional, a small amount of reactivefunctionality can be tolerated to the extent that the moisture uptakecharacteristics of the modifier (as evidenced by, for example,thermogravimetric analysis (TGA)) are not significantly affected.

Useful particulate modifiers can have any of a wide range of particlesizes (as measured prior to addition to the thermosetting resin). Formany applications, however, microparticles can be effectively utilized.Preferred particles can have an average diameter of at least about 0.1micron, 0.2 micron, or 2 microns up to (and including) about 10 microns,50 microns, 100 microns, 200 microns, or 500 microns (where any lowersize limit can be paired with any upper size limit, depending upon theproperties desired for a particular application). (As used herein, theterm “diameter” refers not only to the diameter of substantiallyspherical particles but also to the longest dimension of non-sphericalparticles.) Since the particulate modifiers are preformed, theirparticle size is predetermined, but some change in size can occur uponaddition to the thermosetting resin (for example, due to swelling).

Suitable modifiers include core-shell polymer modifiers having apolymerized rubbery core surrounded by a polymerized thermoplastic orglassy shell, and the like, and mixtures thereof. Useful modifiers ofthese types are described in Polymer Toughening, edited by Charles B.Arends, Chapter 5, pages 131-174, Marcel Dekker, Inc., New York (1996),the descriptions of which are incorporated herein by reference. Usefulmodifiers can also include elastomeric polymer modifiers that lack theabove-described thermoplastic or glassy shell, provided that themodifier is at least somewhat swellable in the selected thermosettingresin while substantially maintaining its discreteness.

Preferred modifiers include core-shell polymer modifiers, and the like,and mixtures thereof. More preferred are core-shell polymer modifiershaving a polyacrylate or polymethacrylate (hereinafter, designatedjointly as poly(meth)acrylate) shell and a synthetic rubber core (mostpreferably, a poly(meth)acrylate shell and a core selected fromstyrene-butadiene rubber, acrylonitrile-butadiene rubber, andcombinations thereof, including copolymers).

Useful glassy shells include those that comprise polymerized acrylicacid ester or methacrylic acid ester (preferably, C₁-C₄alkyl-substituted methacrylate; more preferably, polymethylmethacrylateor a copolymer of alkyl methacrylate and butyl acrylate); polymerizedmonovinyl aromatic hydrocarbon; a polymerized mixture of acrylic ormethacrylic acid ester and monovinyl aromatic hydrocarbon (for example,a copolymer of methyl methacrylate and styrene); and the like; andcombinations thereof.

Useful rubbery cores include those that comprise polyacrylate (forexample, poly(butyl acrylate), poly(isooctyl acrylate), or a copolymerof ethyl acrylate and butyl acrylate); polysiloxane (for example,polydimethylsiloxane); polymerized diene (for example, polybutadiene); apolymerized mixture of diene and monovinyl aromatic hydrocarbon (forexample, a copolymer of butadiene and styrene); a polymerized mixture ofdiene and acrylic monomer (for example, a copolymer of butadiene andacrylonitrile); a polymerized mixture of acrylic or methacrylic acidester and monovinyl aromatic hydrocarbon (for example, a copolymer ofbutyl acrylate and styrene); and the like; and combinations thereof (forexample, copolymers of alkyl methacrylate, butadiene, and styrene).

Useful modifiers include core/shell polymers such asmethacrylate-butadiene-styrene (MBS) copolymer wherein the core iscrosslinked styrene/butadiene rubber and the shell is polymethylacrylate(for example, ACRYLOID KM653 and KM680, available from Rohm and Haas,Philadelphia, Pa.), those having a core comprising polybutadiene and ashell comprising poly(methyl methacrylate) (for example, KANE ACE M511,M521, B11A, B22, B31, and M901 available from Kaneka Corporation,Houston, Tex. and CLEARSTRENGTH C223 available from ATOFINA,Philadelphia, Pa.), those having a polysiloxane core and a polyacrylateshell (for example, CLEARSTRENGTH S-2001 available from ATOFINA andGENIOPERL P22 available from Wacker-Chemie GmbH, Wacker Silicones,Munich, Germany), those having a polyacrylate core and a poly(methylmethacrylate) shell (for example, PARALOID EXL2330 available from Rohmand Haas and STAPHYLOID AC3355 and AC3395 available from Takeda ChemicalCompany, Osaka, Japan), those having an MBS core and a poly(methylmethacrylate) shell (for example, PARALOID EXL2691A, EXL2691, andEXL2655 available from Rohm and Haas); and the like; and mixturesthereof. Preferred modifiers include the above-listed ACRYLOID andPARALOID modifiers; and the like; and mixtures thereof.

(3) Other Components

The curable composition can further comprise one or more additivesincluding, for example, soluble thermoplastic additives (for example, tomodify viscosity or rheology to ensure a handleable film); curingagents; cure accelerators; catalysts; crosslinking agents; dyes; flameretardants; pigments; flow control agents; reinforcing fillers, fibers,or particles (including silica, calcium carbonate, barium sulfate, glassbeads, and the like); electrically or thermally conductive particles;scrim or embedded carrier (for example, woven or nonwoven glass, wovenor nonwoven polymeric fabrics such as those of polyamide or polyester,and metal meshes or foils such as those of aluminum or copper); and thelike; and mixtures thereof. The additives can be, for example, partiallyor wholly embedded in the composition or borne on a surface thereof. Thecomposition itself can also be borne on a carrier (for example, arelease liner).

Epoxide resins can be cured by a variety of curing agents, some of whichare described (along with a method for calculating the amounts to beused) by Lee and Neville in Handbook of Epoxy Resins, McGraw-Hill, pages36-140, New York (1967). Useful epoxide resin curing agents includepolyamines such as ethylenediamine, diethylenetriamine,aminoethylethanolamine, and the like, as well as aromatic amines such asdiaminodiphenylsulfone, 9,9-bis(4-aminophenyl)fluorene,9,9-bis(3-chloro-4-(aminophenyl)fluorene,9,9-bis(3-methyl-4-(aminophenyl)fluorene, and the like; hydrazides suchas isophthalic dihydrazide; amides such as dicyandiamide; polycarboxylicacids such as adipic acid; acid anhydrides such as phthalic anhydrideand chlorendic anhydride; polyphenols such as bisphenol A; and the like;and mixtures thereof. Generally, the epoxide resin and curing agent areused in stoichiometric amounts, but the curing agent can be used inamounts ranging from about 0.1 to 1.7 times the stoichiometric amount ofepoxide resin.

Epoxide resin curing agents also include catalysts (for example, Lewisacids and bases; tertiary amines; thermal cationic catalysts includingBrøsted acids; anionic catalysts including imidazoles such as4,5-diphenylimidazole; complexed Lewis acids; and photocatalystsincluding organometallic compounds and salts). Thermally-activatedcatalysts can generally be used in amounts ranging from about 0.05 toabout 5 percent by weight, based upon the amount of epoxide resinpresent in the curable composition.

N,N′-bismaleimide resins can be cured using diamine curing agents, forexample, such as those described in U.S. Pat. No. 3,562,223 (Bargain etal.), the description of which is incorporated herein by reference.Generally, from about 0.2 to about 0.8 moles of diamine can be used permole of N,N′-bismaleimide. N,N′-bismaleimides can also cure by othermechanisms, for example, co-cure with aromatic olefins (such asbis-allylphenyl ether, 4,4′-bis(o-propenylphenoxy)benzophenone,o,o′-diallyl bisphenol A, and the like) or thermal cure via aself-polymerization mechanism.

Cyanate ester resins can be cyclotrimerized by application of heatand/or by using catalysts such as zinc octoate, tin octoate, zincstearate, tin stearate, copper acetylacetonate, and chelates of iron,cobalt, zinc, copper, manganese, and titanium with bidentate ligandssuch as catechol. Such catalysts can generally be used in amounts offrom about 0.001 to about 10 parts by weight per 100 parts of cyanateester resin.

Preparation of Curable Composition

The curable composition of the method of the invention can be preparedby combining at least one particulate modifier, at least one resin, andany other components (optionally, with stirring or agitation). Theresins can be liquid, solid, or a combination thereof, and thus theresulting composition can be, for example, in the form of a paste or afilm. Depending upon its particular formulation and viscoelasticcharacteristics, such a film can be handled with or without the aid of asupporting material (for example, an embedded scrim or release liner).

Preferably, the particulate modifier can be well-dispersed in the resin,so as to be substantially non-agglomerated. Solvent can be used to aidin combination and dispersion, if desired, provided that the chosensolvent is one that cannot react appreciably with the components of thecomposition and that cannot appreciably dissolve or swell theparticulate modifier (especially the elastomer component(s) of themodifier). Suitable solvents include, for example, acetone, heptane,toluene, isopropanol, and the like, and mixtures thereof.

Preferably, little or no solvent is utilized. Solventless compositionscan be prepared by simply combining the components with or without theuse of mild heating. In a more preferred method of forming the curablecomposition, the components are combined in a solvent-free process,wherein the resultant mixture is both heated and stirred until arelatively uniform mixture is formed.

The particulate modifier can generally be included in the composition ina concentration of about 2 to about 30 weight percent, based upon thetotal weight of the composition. Preferably, the modifier is present ina concentration of about 5 to about 20 weight percent, based upon thetotal weight of the composition.

Preferably, at least one thermally- or photolytically-activatable curingagent is included in the curable composition in order to facilitate lowtemperature processing. Such curing agents are preferably incorporatedinto the composition at temperatures lower than the activationtemperature of the curing agents. Preferred curing agents includeimidazoles, amides (for example, dicyandiamide), aromatic amines,modified ureas, anhydride curing agents, hydrazide curing agents,thermal cationic catalysts, anionic catalysts, photocatalysts, andmixtures thereof. Most preferred are amides, hydrazides, modified ureas,aromatic amines, and mixtures thereof. The further addition of a flowcontrol agent to the curable composition can facilitate the achievementof desired film formation and other Theological characteristics.

In a preferred method, the curable composition can be formed bycombining the particulate modifier(s) and the resin(s) at elevatedtemperatures (for example, temperatures sufficient to melt the resin soas to facilitate its relatively uniform mixing with the modifier) andthen cooling the resulting combination to a temperature below theactivation or melting temperature of the curing agent(s). The curingagent(s) can then be blended into the combination.

Application of Curable Composition

The curable composition used in the method of the invention can beapplied to the composite article (and/or to an adherend, which is a bodythat is to be adhered to the composite article at their interface) byany of a variety of application methods. Useful application methodsinclude, for example, coating (using roll, spray, brush, or extrusiontechniques), lamination, reticulation, vacuum lamination, troweling, andthe like, and combinations thereof. Cutting techniques (for example, diecutting, Gerber cutting using a heated cutting element, and lasercutting) can also be employed to provide particular shapes prior toapplication. At least one of the surfaces to which the composition isapplied is a composite surface. Solvent-free application of thecomposition is preferred and can be accomplished, for example, bytransfer lamination of the composition in film form to a desiredsurface.

In surfacing a composite article, the curable composition can be appliedby, for example, transfer lamination followed by vacuum compaction (ifthe composition is in film form) or by troweling followed by smoothing(if the composition is in paste form). The surfacing method of theinvention can be used to cover surface imperfections (for example, thosecaused by honeycomb mark-off or fiber weave pattern telegraphing) and toprovide a relatively smooth, paintable surface.

In joining the composite article and an adherend, the curablecomposition can be applied to the article directly, or it can be appliedto the article indirectly by, for example, direct application to theadherend to form a composition-bearing adherend, followed by bringingthe article and the composition-bearing adherend together in a mannersuch that the composition is sandwiched between the article and theadherend. Thus, the joining method of the invention can comprise (a)applying an uncured mass of the curable composition (for example, in theform of a film or a paste) to at least one of a polymeric compositearticle and an adherend; (b) sandwiching the uncured mass of the curablecomposition between the article and the adherend; and (c) curing thecomposition to form a joint between the article and the adherend. Ifdesired, such joining method can be carried out by simply inserting thecomposition (for example, in the form of a film) between the article andthe adherend as they are brought together.

Adherends can be chosen from a wide variety of polymeric compositearticles, films, sheets, and other surfaces, depending upon theparticular joining application. The curable composition can formadhesive bonds between a polymeric composite article and metalliccomponents (for example, iron, aluminum, titanium, magnesium, copper,stainless steel, and the like, and alloys thereof) and between apolymeric composite article and non-metallic substrates (for example,reinforced and unreinforced thermoplastic and thermoset polymers, aswell as other organic materials (or organic composite materials) andinorganic materials including glass and ceramics).

Preferably, the adherend comprises a polymeric composite article. Morepreferably, the adherend comprises a polymeric composite article and theresulting joined structure forms at least a portion of a vehicle (mostpreferably, a portion of an aircraft).

Preferred adherends also include those that comprise protectivearticles, paint replacement systems, and/or lightning protectionsystems. Such adherends can comprise, for example, one or more polymericcomposite layers, one or more layers of the curable composition (curedor uncured), one or more layers of metal (for example, metal mesh, whichcan optionally be embedded in the curable composition prior to cure),and/or one or more protective article, paint replacement applique,and/or lightning protection applique layers. Such lightning protectionappliques can comprise, for example, a polymer film (preferably, afluoropolymer film), a pressure-sensitive adhesive (preferably, anacrylic pressure-sensitive adhesive), and a metal layer that canoptionally be embedded in the pressure-sensitive adhesive or bondeddirectly to the polymer film using any of the methods described in theart. Alternatively, the pressure-sensitive adhesive (of the lightningprotection applique, or of a paint replacement applique) can be omittedand optionally replaced with a thermosetting adhesive composition (forexample, the curable composition used in the method of the invention).Useful protective articles, paint replacement appliques, and lightningprotection systems include those described in U.S. Patent ApplicationPublication No. US 2002/0179240 (Clemens et al.), U.S. Pat. No.6,475,616 (Dietz et al.), International Patent Application PublicationNo. WO 99/64235 (Minnesota Mining and Manufacturing Company), U.S. Pat.No. 6,177,189 (Rawlings et al.), U.S. Pat. No. 6,790,526 (Vargo et al.),U.S. Patent Application Publication No. US 2002/0081921 (Vargo et al.),U.S. Pat. No. 4,912,594 (Bannink, Jr. et al.), U.S. Pat. No. 6,432,507(Brick et al.), and European Patent Application Publication No. EP 1 011182 (Minnesota Mining and Manufacturing Company), the descriptions ofwhich are incorporated herein by reference.

The method of the invention can comprise one or more surfacing steps,one or more joining steps, the use of one or more polymeric compositearticles, and/or the use of one or more adherends.

Curing

The curable composition used in the method of the invention isthermosettable. A “thermosettable” or “thermosetting” composition is onethat can be cured (that is, crosslinked) by exposure to, for example,thermal radiation (or heat), actinic radiation, moisture, or other means(preferably, thermal radiation) to yield a substantially infusible (thatis, thermoset) material. Combinations of various curing means can alsobe used (for example, a combination of heat and actinic radiation).

EXAMPLES

Objects and advantages of this invention are further illustrated by thefollowing examples, but the particular materials and amounts thereofrecited in these examples, as well as other conditions and details,should not be construed to unduly limit this invention.

Test Methods

Weight Loss by Thermogravimetric Analysis (TGA)

Cured polymeric composite articles were evaluated for moisture contentusing a Thermogravimetric Analyzer TGA-2950 (available from TAInstruments, New Castle, Del.). The cured article was removed from theconditioning chamber (where applicable) and small pieces were broken offusing a pliers to provide samples which were 2 to 3 plies thick and thatweighed between 4.968 and 19.209 milligrams. These samples wereessentially immediately placed in a small closed vial until tested,between 15 and 30 minutes later. The samples were heated fromapproximately 25° C. to 200° C. at a rate of 110° C./minute in anitrogen atmosphere at a flow rate of from 40 to 60 milliliters/minute.Weight loss over this temperature range was calculated using thesoftware provided with the equipment. Results are reported as % weightloss (of moisture).

Overlap Shear Strength (OLS)

Cured joined structures were evaluated for overlap shear strength. Morespecifically, cured joined structures measuring 7 inches (17.8centimeters) long were obtained which were then cut in the lengthwisedirection into 1 inch (2.54 centimeters) wide (nominal) test strips.Next, one groove was cut in the crosswise direction through thethickness of the cured polymeric composite article on each side of acured joined structure test strip in an offset manner, so as to form a0.5 inch (12.7 millimeters) long overlap section at the center of thetest strip. This formed a test strip similar to that described in ASTM D3165-95, which was then positioned in a tensile tester (available fromMTS Systems Corporation, Eden Prairie, Minn.) such that the grippingjaws were approximately 5 inches (12.7 centimeters) apart and each jawgripped approximately 1 inch (2.5 centimeters) of the test strip. A30,000 pound-force (lb_(f)) (13.3 kiloNewtons) load cell was employed. Agrip separation rate of 0.05 inches/minute (1.27 millimeters/minute) wasapplied until failure occurred. Testing was conducted at one of twodifferent test temperatures (93° C. or 136° C.), as determined by meansof a thermocouple attached to the test strip. Samples were equilibratedat temperature for between 10 and 20 minutes prior to testing. For eachcured joined structure three test strips were evaluated and used toobtain an average value. The results are reported in pounds/square inch(psi) and in MPa.

Environmental Conditioning

Cured polymeric composite articles were conditioned prior to testingusing one of the following methods.

Method 1: Dry

A cured polymeric composite article was dried in an oven at 235° F.(113° C.) for 9 days, then removed and allowed to cool for 1 hour toabout 72° F. (22° C.) after which it was essentially immediately eitherevaluated by thermogravimetric analysis (TGA) or used to prepare a curedjoined structure.

Method 2: Ambient

A cured polymeric composite article was stored at ambient conditions,approximately 72° F. (22° C.) and 50% Relative Humidity (RH), for 21days, after which it was essentially immediately evaluated by TGA.

Method 3: Wet

A cured polymeric composite article was conditioned in atemperature/humidity chamber at 160° F. (71° C.) and 100% RH for 9 days,then allowed to cool on a benchtop to room temperature for approximately30 minutes, after which it was essentially immediately either evaluatedby TGA or used to prepare a cured joined structure.

Materials DER 332 A liquid bisphenol A-based polyepoxide resin having anepoxide equivalent weight of from 171 to 175 grams/equivalent, availableas DER ™ 332 resin from Dow Chemical Company, Midland, Michigan. EPON828 A liquid bisphenol A-based polyepoxide resin having an epoxideequivalent weight of from 185 to 192 grams/equivalent, available asEPON ™ 828 resin from Resolution Performance Products, Houston, Texas.EPON SU-2.5 A liquid bisphenol A-based novolac polyepoxide resin havingan average epoxide group functionality of about 2.5, available as EPON ™SU-2.5 resin from Resolution Performance Products, Houston, Texas. EPONSU-8 A solid bisphenol A-based novolac polyepoxide resin having anaverage epoxide group functionality of about 8, available as EPON ™ SU-8resin from Resolution Performance Products, Houston, Texas. EPON 1004F Amedium molecular weight bisphenol A-based polyepoxide resin having anepoxide equivalent weight of from 800 to 950 grams/equivalent, availableas EPON ™ 1004F resin from Resolution Performance Products, Houston,Texas. EPON 1009F A very high molecular weight solid bisphenol A-basedpolyepoxide resin having an epoxide equivalent weight of from 2300 to3800 grams/equivalent and a melting point of between 130 and 140° C.,available as EPON ™ 1009F resin from Resolution Performance Products,Houston, Texas. TACTIX 756 A dicyclopentadiene-based polyepoxide resin,having an epoxide equivalent weight of from 245 to 265 grams/equivalent,available as TACTIX ™ 756 resin from Huntsman Advanced MaterialsAmericas, Incorporated, Brewster, New York. CG 1400 Dicyandiamide(1-cyanoguanidine)), available as Amicure ™ CG- 1400 from Air Productsand Chemicals, Incorporated, Allentown, Pennsylvania. OMICURE U52 Anaromatic substituted urea (4,4′-methylene-bis(phenyl dimethyl urea),available as OMICURE ™ U52 from CVC Specialty Chemicals Incorporated,Moorestown, New Jersey. DEH 85 An unmodified phenolic hardener having anactive hydrogen equivalent weight of from 250 to 280 grams/equivalent,available as DEH ™ 85 Epoxy Curing Agent from Dow Chemical Company,Midland, Michigan. IPDH Isophthaloyldihydrazide, having an amineequivalent weight of 49.2 grams/equivalent. o-TBAF9,9-bis(3-methyl-4-aminophenyl)fluorene, having a theoretical aminehydrogen equivalent weight of 94.5 grams/equivalent. EXL-2691A Acore/shell impact modifer having a crossliniked poly(butadiene/styrene)core with a grafted poly(methyl methacrylate) shell, available in powderform as PARALOID EXL ™-2691A from Rohm and Haas, Philadelphia,Pennsylvania. DUOMOD 5047 A carboxyl-functional elastomeric powderhaving a target average particle size of 50 micrometers and a targetglass transition temperature of approximately 19° C. (obtained asDuoMod ™ 5047 toughener from Zeon Chemicals L.P., Louisville, Kentucky).DUOMOD 5097 An epoxy-functional elastomeric powder supplied in a fineagglomerate form with at least 99 percent of the agglomerate particleshaving a size of less than 105 micrometers, and with a target individualparticle size of 0.3 micrometers (obtained as DuoMod ™ 5097 toughenerfrom Zeon Chemicals L.P., Louisville, Kentucky). BOLTORN E1 Anepoxy-functional, dendritic, viscous liquid (at room temperature)polymer having a highly branched aliphatic polyester backbone, amolecular weight of approximately 10,500 grams/mole, an epoxy equivalentweight of approximately 850 to 900 grams/equivalent, and an average of11 reactive epoxide groups per molecule, available as BOLTORN ™ E1polymer, an experimental material, from Perstorp Specialty Chemicals AB,Sweden. Rubber Toughener Diprimary amine endcapped poly(tetramethyleneoxide), having a number average molecular weight of about 7500. CTBN #1A liquid, carboxyl-terminated butadiene/nitrile rubber polymer, having amolecular weight of about 3800, a glass transition temperature of −66°C., and a carboxyl content of 28 (acid number), available as HYCAR ™CTBN 1300x31 from Noveon, Incorporated, Cleveland, Ohio. CTBN #2 Aliquid, carboxyl-terminated butadiene/nitrile rubber polymer, having amolecular weight of about 3150, a glass transition temperature of −30°C., and a carboxyl content of 32 (acid number), available as HYCAR ™CTBN 1300x13 from Noveon, Incorporated, Cleveland, Ohio. VTBN A liquid,vinyl-terminated butadiene/nitrile rubber polymer, having a Brookfieldviscosity of 425,000 mPa-sec at 27° C. and a glass transitiontemperature of −45° C., available as HYCAR ™ VTBN 1300x43 from Noveon,Incorporated, Cleveland, Ohio. P1800 A powdered grade of polysulfonethermoplastic polymer having a glass transition temperature of 185° C.,available as UDEL ™ P1800 from Solvay Advanced Polymers, LLC,Alpharetta, Georgia. TWARON TWARON ™ 2091 aramid microfibers(poly-(paraphenylene Aramid Pulp terephthalamide)), having a linearmolecular skeleton structure, available in pulp form from TEIJIN TWARONBV, The Netherlands. AF-163-2M 3M ™ Scotch-Weld ™ Structural AdhesiveFilm having a non- woven supporting carrier, based on a modifiedthermosetting epoxy structural adhesive designed for curing attemperatures of 225° F. (107° C.) to 300° F. (149° C.), available from3M Company, St. Paul, Minnesota. AF-3109-2K 3M ™ Scotch-Weld ™Structural Adhesive Film having a knit scrim support, based on anonvolatile, modified thermosetting epoxy structural adhesive designedfor curing at temperatures of 225° F. (107° C.) to 350° F. (177° C.) andhaving an areal weight of 0.80 to 0.90 pounds/square foot (390 to 439grams/square meter), available from 3M Company, St. Paul, Minnesota.AF-191 3M ™ Scotch-Weld ™ Structural Adhesive Film; an unsupported,thermosetting, nonvolatile, modified epoxy film adhesive designed forcuring at a temperature of 350° F. (177° C.) and having an areal weightof 0.05 pounds/square foot (244 grams/square meter)), available from 3MCompany, St. Paul, Minnesota. AF-325 3M ™ Scotch-Weld ™ Low DensityComposite Surfacing Film; a non-woven polyester supported, lowvolatility, thermosetting epoxy film for composite surfacing, designedfor curing at temperatures of 250° F. (121° C.) to 350° F. (177° C.) andhaving an areal weight of between 147 and 195 grams/square meter,available from 3M Company, St. Paul, Minnesota.

Preparation of Curable Resin Compositions

Two different preblends of polyepoxide resin and flow modifier wereprovided and used to prepare curable resin compositions:

Preblend #1: 92.4 grams of EPON 1004F was placed into a 150 milliliterreactor and heated to approximately 230° F. (110° C.) using a paddleblade at approximately 200 revolutions per minute (rpm) for constantagitation until the polyepoxide resin was essentially completely melted.Then 7.6 grams of TWARON™ 2091 aramid fiber flow modifier was added tothe polyepoxide resin and mixed for 15 minutes. The dispersion that wasobtained was removed from the reactor and placed on a silicone-treatedrelease liner and allowed to cool to room temperature for approximately3 hours. The resulting solid material was then ground using amicro-pulverizing type hammer mill having a 0.38 inch (9.5 millimeters)diameter screen. The maximum particle size was 0.38 inch (9.5millimeters) in diameter. The majority of the particles had asignificantly smaller diameter.

Preblend #2: 150 grams of EPON 828 was placed into a 250 milliliterreactor and heated to approximately 200° F. (93° C.) using a paddleblade at approximately 200 rpm for constant agitation. Next, 30 grams ofP1800 polysulfone resin flow modifier was slowly added to thepolyepoxide resin. The temperature was then increased to approximately350° F. (177° C.) and the agitation speed reduced to approximately 150rpm. The dispersion was heated and agitated under these conditions untilit became a substantially homogeneous mixture. This mixture was allowedto cool to room temperature to provide a viscous, yellow-colored,transparent liquid.

Polyepoxide resins and the above-described preblends were charged into a200 gram capacity plastic container in the appropriate ratios to providethe amounts shown for the various Examples in Table 1 below. Thecontainer was heated for about 15 minutes in a forced air oven set at150° C., after which it was removed and placed in a planetary-type mixer(SPEED MIXER™, Model DA 400 FV, available from Synergy Devices Limited,Buckinghamshire, United Kingdom) set at a speed of 2750 rpm for 1minute. The container and its contents were then returned to the ovenand equilibrated at about 120° C. for between 15 and 20 minutes. Next, atoughening modifier was added to this blend, and it was mixed asdescribed above, after which the container was removed from theplanetary mixer and allowed to cool below 100° C. The curing agents werethen added, and the blend was again mixed as described above. Afterremoval from the mixer, the inside wall of the container was scrapeddown, followed by putting the container back into the mixer for anothercycle. The curable resin composition obtained was used essentiallyimmediately to prepare a curable, liner-supported adhesive film.

Preparation of Curable, Liner-Supported Adhesive Films

The heated composition (having a temperature of about 90° C. (194° F.))from the “Preparation of Curable Resin Compositions” procedure above wascoated between two 0.005 inch (0.13 millimeters) thick paper liners,each having a silicone coating on one side and a polyethylene coating onthe opposite side, such that the curable resin composition contacted thesilicone-coated side of each liner. This was done using a knife-over-bedcoating station having a gap setting of 0.008 inches (0.20 millimeters)greater than the total combined release liner thickness and a bed andknife temperature of 194° F. (90° C.). A liner-supported, curableadhesive film was obtained as a liner/curable adhesive film/linersandwich, which was stored for 24 hours at room temperature (about 72°F. (22° C.)), and then stored at −20° F. (−29° C.) until it was used toprepare curable, nylon fabric-supported adhesive films.

Preparation of Curable, Nylon Fabric-Supported Adhesive Films

A sample of a liner/curable adhesive film/liner sandwich wasequilibrated at room temperature prior to use. The liner from one sideof the sandwich, measuring about 11.5 inches (29.2 centimeters) long andabout 6 inches (15.2 centimeters) wide, was removed, and a supporting,nonwoven nylon fabric (available as Cerex™ 23 fabric, with a roundfilament geometry, from Cerex Advanced Fabrics. L.P., Cantonment, Fla.)having an areal weight of 0.4 ounces/square yard (13.6 grams/squaremeter), which had been corona treated on both sides, was placed on theexposed adhesive surface. This fabric was slightly larger in size thanthe sandwich. The liner was replaced over the nonwoven nylon fabric, andthe resulting lay-up was passed between two rubber-coated, heated niprollers at a temperature of approximately 140° F. (60° C.). The positionof the upper roller and its contact pressure with the lower drive rollerwas controlled by air pressurized pistons having an air supply pressureof about 20 psi (137.9 kPa). A curable adhesive film having a nonwovennylon fabric embedded therein, and having a release liner on each side,was obtained. Curable, nylon fabric-supported adhesive films prepared inthis manner were subsequently used in the Examples described below.

Cured Polymeric Composite Articles

Cured, unidirectional carbon fiber reinforced polymeric compositearticles were provided in two different manners. In the first manner(hereinafter, designated “Source 1”), carbon fiber prepreg material wasobtained and cured into unidirectional carbon fiber reinforced polymericcomposite articles as next described. More specifically, ten plies ofcarbon fiber prepreg (available as “Toray 3900-2/T800S”, having an arealweight of 190 grams/meter² and a resin content of 35%, from Toray CarbonFibers America, Incorporated, Decatur, Ala.) measuring 8 inches by 6inches (20.3 centimeters by 15.2 centimeters), were laid upunidirectionally, and a layer of “Polyester Release Peel-Ply Fabric”protective material (Style 56009, Code 60001, having an areal weight of2.5 ounces/square yard (8.5 grams/square meter) and a nominal thicknessof 0.0055 inches (0.140 millimeters), available from Precision FabricsGroup, Incorporated, Greensboro, N.C.) was positioned on the upper outermajor surface of the resulting construction. The “Polyester ReleasePeel-Ply Fabric” protective material is hereinafter referred to as“Peel-Ply”. This layup was placed in a vacuum bag, which was thenpositioned in an autoclave. A partial vacuum of about 1.9 inches (48.3mm) Hg was applied at room temperature (approximately 72° F. (22° C.))for 10 to 15 minutes, after which the external pressure was graduallyincreased to 85 psi (586 kPa). The vacuum bag was then vented to releasethe vacuum, and the temperature was raised at 5° F./minute (2.8°C./minute) up to 350° F. (177° C.) and held there for 2 hours. The curedpolymeric composite article with “Peel-Ply” on one surface was thencooled at 10° F./minute (5.5° C./minute) to room temperature, at whichpoint the pressure was released, and the cured article having anapproximate thickness (not including the “Peel-Ply” layer) of 0.075inches (1.9 millimeters) was removed from the autoclave and vacuum bag.

In the second manner (hereinafter, designated “Source 2”), curedpolymeric composite articles measuring approximately 12 inches by 6inches by 0.075 inches (30.5 centimeters by 15.2 centimeters by 1.9millimeters) were obtained. These cured composite articles had beenprepared using both the prepreg material and essentially the sameprocedure as described above. The cured articles had a layer of“Peel-Ply” protective material on one of their two major outer surfaces.The thickness of these articles was measured without the “Peel-Ply” inplace.

Preparation of Cured Joined Structures

Cured joined structures, prepared from the above-described curable nylonfabric-supported adhesive film and two of the above-described curedpolymeric composite articles, were provided for evaluation of overlapshear strength. More specifically, two cured polymeric compositearticles measuring 6 inches by 12 inches (15.2 centimeters by 30.5centimeters), or 6 inches by 8 inches (15.2 centimeters by 20.3centimeters) were conditioned in one of the ways described above in“Environmental Conditioning”. The “Peel-Ply” protective material wasthen removed from the conditioned articles. After removing theprotective liner from one side of the curable nylon fabric-supportedadhesive film, the film was applied to the entire surface of aconditioned article, from which the “Peel-Ply” had been removed, by handusing a small rubber roller in such a manner as to exclude entrapped airand ensure intimate contact between the exposed adhesive and thearticle. After removing the second liner from the curable adhesive film(and the “Peel-Ply” from a second cured polymeric composite article),the newly exposed surface of the second composite article was placed incontact with the exposed adhesive surface to give a sandwich assemblywith a cured polymeric composite article on each side of the curableadhesive film, the articles and film all having the same length andwidth dimensions. Next, the resulting assembly was fastened togetherusing a pressure-sensitive adhesive tape at each end and then placed ona vacuum table for 15 minutes at full vacuum. The assembly was thencured in an autoclave in the following manner. After applying a vacuumto reduce the pressure to about 1.9 inches (48.3 mm) Hg, an externalpressure of about 45 psi (310 kPa) was applied, and the temperature ofthe autoclave was heated from about room temperature (72° F. (22° C.))to either 250° F. (121° C.) or 350° F. (177° C.), depending on theparticular adhesive film employed, at a rate of 4.5° F./minute (2.5°C./minute). The vacuum was released when the pressure reached about 15psi (103.4 kPa). The final temperature and pressure were maintained for120 minutes before cooling to room temperature at a rate of 5° F./minute(2.8° C./minute), at which point the pressure was released and a curedjoined structure was obtained.

Cured Composite Article with a Surfacing Layer

An aluminum panel surface was polished with fine steel wool, thencleaned with methyl ethyl ketone (MEK). Masking tape was applied to theouter edges of the panel surface, and the panel surface was then wipedwith release agent Loctite™ Frekote™ 700-NC Mold Release Agent (awater-based release agent available from Loctite Corporation, RockyHill, Conn.), which was allowed to air dry after which the masking tapewas removed. The resulting release coating was then cured at 250° F. for30-60 min. After cooling to room temperature, the panel surface waspolished with a lint free cloth (Kimwipes™ EX-L, available fromKimberly-Clark Corporation, Rosswell, Ga.). Next, after removal of thepaper liner from one side, a curable nylon fabric-supported adhesivefilm measuring approximately 8 inches by 6 inches (20.3 centimeters by15.2 centimeters) was positioned such that its newly exposed surfacecontacted the polished panel inside the edges that had been masked off.The adhesive film was rolled down using a rubber roller. Paper liner wasremoved from the second, upper side of the adhesive film, and a curedcomposite article, measuring approximately 8 inches by 6 inches (20.3centimeters by 15.2 centimeters), was placed on the exposed, top surfaceof the adhesive film. This assembly was then placed on a vacuum tablefor 15 minutes at full vacuum. Next, the assembly was positioned in avacuum bag and cured in an autoclave in the following manner. Afterapplying a vacuum to reduce the pressure to about 1.9 inches (48.3 mm)Hg, an external pressure about 45 psi (310 kPa) was applied, and thetemperature of the autoclave was heated from about room temperature (72°F. (22° C.)) to either 250° F. (121° C.) or 350° F. (177° C.), dependingupon the particular adhesive film employed, at a rate of 4.5° F./minute(2.5° C./minute). The vacuum was released when the pressure reachedabout 15 psi (103.4 kPa). The final temperature and pressure weremaintained for 120 minutes before cooling to room temperature at a rateof 5° F./minute (2.8° C./minute), at which point the pressure wasreleased and, upon removal from the aluminum panel, a cured compositearticle having a surfacing layer on one side was obtained. The curedcomposite article with surfacing layer was evaluated visually by eye forgeneral appearance (for example, as to uniformity and surfacesmoothness) and pin holes (for example, as to quantity and size). Avalue of 1 (worst) to 10 (best) was assigned for each characteristic foreach article evaluated.

Cured Composite Article with Lightning Protection System

An aluminum panel surface was polished with fine steel wool, cleanedwith methyl ethyl ketone (MEK), then polished with a lint-free cloth(Kimwipesm™ EX-L, available from Kimberly-Clark Corporation, Rosswell,Ga.). A gray fluoropolymer film, having both surfaces etched, wasprovided by coextruding a uniform mixture of pellets having 97 percent(by weight) clear DYNEON THV 500 (atetrafluoroethylene-hexafluoropropylene-vinylidene fluoride terpolymer,available from Dyneon (a wholly owned subsidiary of 3M Company),Oakdale, Minn.) and 3 percent (by weight) of gray pigmented DYNEON THV200 as described in U.S. Pat. No. 6,475,616 (Dietz et al.), Example 1. Asolvent-based acrylic pressure sensitive adhesive was applied to oneside of the fluoropolymer film and dried to give a 0.0003 inch (about0.008 millimeters) thick adhesive layer. Next, an aluminum mesh (PartNo. 1.5AL6-075F, having areal weight of 0.0075 pounds/square foot (36.6grams/square meter) and an overall thickness of 0.0015 inches (0.038millimeters), available from Dexmet Corporation, Naugatuck, Conn.) waslaminated, at room temperature, onto the acrylic adhesive surface. Asecond layer of the solvent-based acrylic pressure sensitive adhesivewas applied on top of the aluminum mesh and dried to give afluoropolymer film having a pressure sensitive acrylic adhesive layerwith an embedded aluminum mesh on one side. The total adhesive layerthickness, including the mesh, was about 0.003 inches (0.08millimeters). A low density polyethylene (LDPE) protective liner wasplaced over the adhesive layer.

The resulting coated fluoropolymer film was positioned on the aluminumpanel with the protective liner layer facing outward. Next, theprotective liner was removed to expose the acrylic adhesive surface, andthe first protective liner from one side of a 350° F. (177°) curable,nylon fabric-supported adhesive film was removed to expose one surfaceof the curable adhesive film. The two exposed surfaces were brought intocontact with each other and the combined structure was rubbed down byhand to remove any wrinkles and ensure intimate contact between theacrylic adhesive layer and the curable adhesive film. The secondprotective liner was removed from the top side of the curable, nylonfabric-supported adhesive film and, after removal of their respectiveprotective liners, two plies of fiberglass prepreg material (Part No.PP500H, available from Critical Materials Incoporated, Poulsbo, Wash.)were placed on the exposed curable adhesive surface. A second sheet ofcurable, nylon fabric-supported adhesive film was provided and, afterremoval of the protective liner from one side of it, the exposed surfaceof this second sheet was applied by hand to the second outer, exposedsurface of prepreg material and rubbed down by hand as described above.Next, after removal of the second protective liner from the secondcurable, nylon fabric-supported adhesive film, the exposed surface ofthe adhesive film was brought into contact with a glass fabricreinforced honeycomb structure impregnated with phenolic resin (HexWeb™HRP-3/16-8.0, available from Hexcel Corporation, Stamford, Conn.). Afterremoval of the appropriate protective liners, another layer of curable,nylon matte-supported adhesive film was applied to the opposite side ofthe honeycomb structure and an additional two plies of fiberglassprepreg were positioned on the outside surface of this curable adhesivefilm. Finally, a layer of “Peel Ply” was placed on the outer, exposedprepreg surface.

This entire assembly was then placed on a vacuum table for 5-10 minutesat full vacuum for compaction. The compacted assembly was thenpositioned in a vacuum bag and cured in an autoclave in the followingmanner. After applying a vacuum to reduce the pressure to about 1.9inches (48.3 mm) Hg, an external pressure of about 45 psi (310 kPa) wasapplied, and the temperature of the autoclave was heated from about roomtemperature (72° F. (22° C.)) to 350° F. (177° C.) at a rate of 4.5°F./minute (2.5° C./minute). The vacuum was released when the pressurereached about 15 psi (103.4 kPa). The final temperature and pressurewere maintained for 120 minutes before cooling to room temperature at arate of 5° F./minute (2.8° C./minute), at which point the pressure wasreleased and a cured composite article having a lightning protectionsystem was obtained.

Examples 1-3 and Comparative Examples 1-9

Examples 1-3 and Comparative Examples (CE) 1-9 in Tables 1, 3, and 4below demonstrate the effect of various toughening modifiers in joiningenvironmentally conditioned cured polymeric composite articles togetherto provide cured joined structures. The amounts are given in parts byweight (pbw), wherein the combined amounts of all components is between99 and 102 pbw.

Example 1 and Comparative Example 1 were prepared as described in“Preparation of Cured Joined Structures” above using a 250° F. (121° C.)cure cycle and then evaluated at 200° F. (93° C.) for overlap shearstrength (OLS). Examples 2 and 3, and Comparative Examples 2-9, wereprepared as described in “Preparation of Cured Joined Structures” aboveusing a 350° F. (177° C.) cure cycle and then evaluated at 277° F. (136°C.) for overlap shear strength.

TABLE 1 Formulations Component Ex. 1 Ex. 2 Ex. 3 CE 1 CE 2 CE 3 CE 4 CE5 CE 6 CE 7 CE 8 CE 9 EPON 828 35.0 15.0 15.7 AF- 11.0 15.0 15.0 15.015.0 15.0 15.0 AF- DER 332 10.3 5.85 163-2 2.0 3109-2 EPON 13.7 10.010.0 10.0 10.0 1004F EPON 10.0 10.0 10.0 1009F EPON 25.0 25.0 25.0 25.025.0 25.0 25.0 SU-2.5 EPON 5.12 13.2 SU-8 TACTIX 25.0 25.1 26.4 25.025.0 25.0 25.0 25.0 25.0 756 CG 1400 3.9 4.04 0.093 0.092 4.04 4.04 4.043.93 3.93 3.93 OMICURE 2.1 U52 DEH 85 18.5 IPDH 4.73 4.73 4.73 4.73 4.614.61 4.61 o-TBAF 34.0 33.4 EXL 2691A 14.9 15.0 15.7 3.0 DUOMOD 15.0 5097DUOMOD 15.0 5047 BOLTORN 15.0 E1 Rubber 8.6 Toughener CTBN #1 15.0 CTBN#2 15.0 VTBN 15.0 P1800 3.0 1.37 1.38 3.0 3.0 3.0 3.0 3.0 3.0 TWARON 1.6Aramid Pulp

Moisture Content of Cured Polymeric Composite Articles

Cured polymeric composite articles were provided in the two waysdescribed previously. After environmental conditioning, they wereevaluated as described in the test method “Weight Loss.” Thedesignations “Dry”, “Ambient” and “Wet” in the tables refer to theenvironmental conditions to which the cured polymeric composite articleswere exposed. The results are shown in Table 2 below.

TABLE 2 Cured Polymeric % Weight Loss Composite Article Dry Ambient WetSource 1 0.377 Not Determined 1.334 Source 2 0.267 0.508 1.101 Average0.322 0.508 1.218

Overlap Shear Strength (OLS) of Cured Joined Structures

Environmentally conditioned cured polymeric composite articles werebonded together using the adhesive films of Examples 1-3 and ComparativeExamples 1-9 to provide cured joined structures which were thenevaluated for overlap shear strength (OLS). The designations “Dry” and“Wet” in the tables refer to the environmental conditions to which thecured polymeric composite articles were exposed just prior to bondingwith the adhesive films. % Retention was calculated as [OLS (Wet)/OLS(Dry)]×100.

TABLE 3 OLS (psi) [MPa] Example No. Dry Wet % Retention Ex. 1 2100[14.5] 1032 [7.1] 49 CE 1 3365 [23.2]  531 [3.7] 16

TABLE 4 Example OLS (psi) [MPa] No. Dry Wet % Retention 2 3448 [23.8]2113 [14.6] 61 3 3603 [24.8] 2441 [16.8] 68 CE 2 3791 [26.1] 956 [6.6]25 CE 3 3536 [24.4] 1668 [11.5] 47 CE 4 3688 [25.4] 866 [6.0] 23 CE 51829* [12.6]  1009* [7.0]   55* CE 6 1560 [10.8] 350 [2.4] 22 CE 7 2398[16.5] 672 [4.6] 28 CE 8 1790 [12.3] 200 [1.4] 11 CE 9 1590 [11.0] 173[1.2] 11 *For CE 5, the resin composition, adhesive film, and curedjoined structure appeared to exhibit gross phase separation of thetoughening modifier, a feature that can compromise overlap shearstrength performance. As a result, the dry OLS value may be low, leadingto an artificially high retention value.

Examples 4 and 5 and Comparative Examples 10 and 11

Adhesive films were used to prepare cured composite articles having acured surfacing layer thereon, which were then evaluated for generalappearance and pin holes, all as described in “Cured Composite Articlewith a Surfacing Layer” above. The results are shown in Table 5 below.AF-325 (CE 11) is an epoxy adhesive film sold specifically as acomposite surfacing film. AF-191 (CE 10) is a commercially availableadhesive film often used for this same purpose.

TABLE 5 General Example No. Adhesive System Appearance Pin Holes CE 10AF-191 9 10 CE 11 AF-325 8 9 4 Example 1 7 5 5 Example 2 9 8

Example 6

The adhesive film of Example 2 above was used to prepare a curedcomposite article having an embedded aluminum mesh therein. Such aconstruction has utility as a means of providing lightning strikeprotection. The article was prepared as described in “Cured CompositeArticle with Lightning Protection” above. The resulting cured compositearticle had a surface that was essentially smooth and had no visibledefects, such as pinholes.

The referenced descriptions contained in the patents, patent documents,and publications cited herein are incorporated by reference in theirentirety as if each were individually incorporated. Variousunforeseeable modifications and alterations to this invention willbecome apparent to those skilled in the art without departing from thescope and spirit of this invention. It should be understood that thisinvention is not intended to be unduly limited by the illustrativeembodiments and examples set forth herein and that such examples andembodiments are presented by way of example only with the scope of theinvention intended to be limited only by the claims set forth herein asfollows.

1. A method comprising (a) providing a cured or curable polymericcomposite article; (b) providing a curable composition comprising (1) atleast one thermosetting resin, and (2) at least one preformed,substantially non-functional, particulate modifier comprising at leastone elastomer; wherein the curable composition contains no liquid rubberpolymer, and (c) directly or indirectly applying said composition to atleast a portion of at least one surface of said article.
 2. The methodof claim 1, wherein said article is a cured polymeric composite article.3. The method of claim 1, wherein said thermosetting resin is selectedfrom the group consisting of epoxide resins, maleimide resins, cyanateester resins, and mixtures thereof.
 4. The method of claim 3, whereinsaid thermosetting resin is an epoxide resin.
 5. The method of claim 1,wherein said modifier is a core-shell polymer modifier.
 6. The method ofclaim 5, wherein said core-shell polymer modifier has a polyacrylateshell and a synthetic rubber core.
 7. The method of claim 1, whereinsaid modifier is in the form of microparticles.
 8. The method of claim1, wherein said modifier is included in said curable composition in aconcentration of about 2 to about 30 weight percent, based upon thetotal weight of said curable composition.
 9. The method of claim 1,wherein said method further comprises bringing at least a portion of atleast one surface of at least one adherend into contact with saidcomposition in a manner such that said composition becomes sandwichedbetween said article and said adherend.
 10. The method of claim 9,wherein said adherend comprises at least one of a polymeric compositearticle, a protective article, a paint replacement system, and alightning protection system.
 11. The method of claim 10, wherein saidpaint replacement system comprises a paint replacement applique and saidlightning protection system comprises a lightning protection applique.12. The method of claim 1, wherein said method further comprises atleast partially curing the composition.
 13. The method of claim 9,wherein said method further comprises at least partially curing thecomposition.
 14. The method of claim 1, wherein said thermosetting resinis an epoxide resin and said modifier is a core-shell polymer modifier.15. A method comprising (a) applying an uncured mass of a curablecomposition to at least one of a polymeric composite article and anadherend said curable composition comprising (1) at least onethermosetting resin, and (2) at least one preformed, substantiallynon-functional, particulate modifier comprising at least one elastomer;wherein the curable composition contains no liquid rubber polymer; (b)sandwiching said uncured mass of said curable composition between saidarticle and said adherend; and (c) curing said composition to form ajoint between said article and said adherend.
 16. A structure comprising(a) a cured or curable polymeric composite article; and (b) a cured orcurable composition comprising (1) at least one thermosetting resin, and(2) at least one preformed, substantially non-functional, particulatemodified comprising at least one elastomer; wherein the cured or curablecomposition contains no liquid rubber polymer; said composition being incontact with at least a portion of at least one surface of said article.17. The structure of claim 16, wherein said article is a cured polymericcomposite article.
 18. The structure of claim 16, wherein saidthermosetting resin is selected from the group consisting of epoxideresins, maleimide resins, cyanate ester resins, and mixtures thereof.19. The structure of claim 18, wherein said thermosetting resin is anepoxide resin.
 20. The structure of claim 16, wherein said modifier is acore-shell polymer modifier.
 21. The structure of claim 20, wherein saidcore-shell polymer modifier has a polyacrylate shell and a syntheticrubber core.
 22. The structure of claim 16, wherein said modifier is inthe form of microparticles.
 23. The structure of claim 16, wherein saidmodifier is included in said cured or curable composition in aconcentration of about 2 to about 30 weight percent, based upon thetotal weight of said composition.
 24. The structure of claim 16, whereinsaid composition is at least partially lured.
 25. The structure of claim16, wherein said structure is a joined structure that further comprisesat least one adherend that is joined to said article by at least onejoint comprising said cured composition.
 26. The structure of claim 25,wherein said adherend comprises at least one of a polymeric compositearticle, a protective article, a paint replacement system, and alightning protection system.
 27. The structure of claim 26, wherein saidpaint replacement system comprises a paint replacement applique and saidlightning protection system comprises a lightning protection applique.28. The structure of claim 16, wherein said thermosetting resin is anepoxide resin and said modifier is a core-shell polymer modifier.